Most membrane and secretory proteins are glycosylated. In many cases, the presence and characteristics of oligosaccharides impact folding, stability, location, ligand interaction, and biological activity of glycoproteins. For example, antibodies typically have complex N-linked oligosaccharides. These can be highly heterogeneous due to variations in levels of fucose, mannose, galactose, N-acetylglucosamine, and/or sialic acid in complex oligosaccharide chains (Jefferis, Trends Pharm. Sci. 30(7):356-362, 2009).
Serum and recombinant antibodies typically contain a mixture of glycoforms. Certain antibody glycoforms have been observed to have a higher affinity for Fc receptors on leukocytes such as Fc gamma RI, Fc gamma RII, Fc gamma RIII, and C1q, which in turn can alter effector function. Antibodies with oligomannose-type oligosaccharides display enhanced antibody dependent cell mediated cytotoxicity (ADCC) and reduced C1q binding (Crispin et al., J. Mol. Biol. 387:1061-1066, 2009). Removal of galactosylation reduces C1q binding and binding to other Fc receptors (Crispin et al., supra; Kobata, Biochim. Biophys. Acta 1780:472-478, 2008). Terminal sialic acids have been shown to reduce the affinity of antibodies for Fc gamma receptors (Jefferis, Nat. Rev. Drug. Disc. 8:226-234, 2009; Walsh et al., Nat. Biotech. 24(10):1241-1252, 2006).
Antibody forms lacking fucose on the primary core N-acetylglucosamine have increased affinity for Fc gamma RIIIa as compared to core-fucosylated forms, and also have an increased ability to trigger ADCC (Jefferis, Exp. Opin. Biol. Ther. 7(9):1401-1413, 2007; Okazaki et al., J. Mol. Biol. 336:1239-1249, 2004; Shibata-Koyama et al., Glycobiol. 19(2): 126-134, 2009). Afucosylated forms have comparable affinity for antigen, C1q, Fc gamma RI, the neonatal Fc receptor (FcRn) and slightly higher affinity for Fc gamma RIIa and Fc gamma RIIb, as compared to fucosylated forms (Jefferis, Exp. Opin. Biol. Ther. 7(9):1401-1413, 2007; Satoh et al., Exp. Opin. Biol. Ther. 6(11):1161-1173, 2006; Kobata, supra). Afucosylated forms of rituximab and trastuzumab have enhanced in vitro and ex vivo ADCC (Jefferis, Exp. Opin. Biol. Ther. 7(9):1401-1413, 2007; Jefferis, Trends Pharm. Sci. 30(7):356-362, 2009; Satoh, supra). Fc gamma RI, Fc gamma RII, Fc gamma RIII, and C1q receptors have been reported to interact with the hinge or hinge proximal region of Fc polypeptides. The increased affinity of afucosylated IgG Fc for Fc gamma RIII may be due to a conformational change in the Fc that reduces steric inhibition of binding (Kobata, supra; Satoh, supra).